Epidemics and pandemics

Epidemics are outbreaks of disease of bacterial or viral origin that involve many people in a localized area at the same time. An example of an epidemic is the hemorrhagic fever outbreak caused by the Ebola virus in Zaire in 1976. When Ebola fever occurs, it tends to be confined to a localized area, and can involve many people. If an outbreak is worldwide in scope, it is referred to as a pandemic. The periodic outbreaks of influenza can be pandemic.

Some maladies can be both epidemic and pandemic. This can be a function of time. An example is Acquired Immunodeficiency Syndrome (AIDS ). Initially, the acknowledged viral agent of AIDS, the Human Immunodeficiency Virus (HIV ), was prevalent in a few geographic regions, such as Haiti, and among certain groups, such as homosexual men in the United States. In these regions and populations, the infection was epidemic in scope. Since these early days, AIDS has expanded to become a worldwide disease that cuts across all racial, cultural, economic and geographic categories. AIDS is now a pandemic.

Influenza can also be epidemic or pandemic. In this case, the antigenic composition of the viral agent of the disease determines whether the virus becomes global in its distribution or not. Antigenic variants of the virus that are quite different from varieties that have preceded it, and so require an adaptive response by the immune system before the infection can be successfully coped with, tend to become pandemic.

Pandemics of influenza can be devastating. The huge number of people who become ill can tax the capability of a regions' or countries' health infrastructure. The preparation to attempt to thwart an influenza pandemic is immense. For example, the preparation and distribution of the required vaccine , and the subsequent inoculation of those who might be at risk, is a huge undertaking. In human terms, influenza pandemics exact a huge toll in loss of life. Even thought the death rate from influenza is typically less than one percent of those who are infected, a pandemic involving hundreds of millions of people will result in a great many deaths.

Epidemics and pandemics have been a part of human history for millennia. An example of this long-standing presence is cholera. Cholera is an infection that is caused by a bacterium called Vibrio cholerae. The bacterium is present in the feces, and can be spread directly to drinking water, and to food via handling of the food in an unhygienic manner. The resulting watery diarrhea and dehydration, which can lead to collapse of body functions and death if treatment is not prompt, has devastated populations all over the world since the beginning of recorded history. The first reports that can be identified as cholera date back to 1563 in India. This and other epidemics in that part of the world lead to the spread of the infection. By 1817 cholera had become pandemic. The latest cholera pandemic began in 1961 in Indonesia. The outbreak spread through Europe, Asia, Africa, and finally reached South America in the early 1990s. In Latin America, cholera still causes 400,000 cases of illness and over 4000 deaths each year.

Influenza is another example of am illness that has been present since antiquity. Indeed, the philosopher Hippocrates first described an influenza outbreak in 412 B.C. There were three major outbreaks of influenza in the sixteenth century (the one occurring in 1580 being a pandemic), and at least three pandemics in the eighteenth century. In the twentieth century there were pandemics in 1918, 1957, and 1968. These were caused by different antigenic types of the influenza virus. The 1918 pandemic is thought to have killed some 30 million people, more than were killed in World War I.

A common theme of epidemics and pandemics throughout history has been the association of outbreaks and sanitary conditions. Inadequate sanitation has and continues to be the breeding ground for the bacteria and viruses that can sweep through populations. The gathering of people in the burgeoning cities of seventeenth and eighteenth century Europe lead to a series of epidemics. These included typhus , typhoid fever , plague, smallpox , dysentery , and cholera. Outbreaks are less of a problem in modern day cities, due to better sanitation conditions and standards of housing. However, in underdeveloped areas of the world, or even in the developed world where sanitation and housing conditions are deficient, such diseases are still present.

Epidemics and pandemics can be so devastating that they can alter the course of history. An example is the Black Plague that spread through Europe and Britain in the seventeenth century. An estimated one-third of the population of Europe was killed, and cities such as London became nearly deserted, as those who could afford to do so fled the city. In the Crimean War (1853–1856), more than 50,000 soldiers died of typhus, while only 2,000 soldiers were actually killed in battle. As a final example, the spread of the plague to the New World by contaminated blankets aboard French sailboats that docked at Halifax, Nova Scotia, in 1746, lead to the decimation of the aboriginal inhabitants of North America.

Within the past several decades, there has been an increasing recognition that disease that were previously assumed to be of genetic or other, nonbacterial or nonviral origin are in fact caused by microorganisms has lead to the recognition that there may be an epidemic or pandemic or maladies such as stomach ulcers and heart disease. These diseases differ from other bacterial and viral epidemics and pandemics, because they do not appear and fade over a relatively short time. Rather, the stomach ulcers caused by the bacterium Helicobacter pylori and the heart disease caused by the reaction of the immune system to infection by the bacterium Chlamydia are so-called chronic infections. These infections are present for a long time, essentially causing a non-stop pandemic of the particular malady.

See also Bacteria and bacterial infections; Bubonic plague; Flu, Great flu epidemic of 1918